The invention is directed to a method of recognizing, by means of an active search head, decoys serving to disguise a target and located in positions which are laterally and vertically offset from the target, as well as to a device for performing the method.
In accordance with methods and devices which do not belong to the state of the art, in a missile equipped with a search head, such as disclosed, for example, in U.S. Pat. No. 3,618,096, the discrimination between the target, for example a ship, and a decoy is effected, in addition to the search for the target in the azimuth plane, by continuously measuring the elevation angle between, for example, the horizontal trajectory of the missile and the line connecting the missile and the target which is actually acquired by the search head. Insofar as this angle differs from zero and, as viewed counterclockwise, becomes positive, the search is interrupted and adjusted to a new target.
In the missiles under consideration, the elevation angle is measured, for example, by radar direction finding. As it is impossible, for technical reasons, to produce a radar beam with a zero degree flare angle, and which is not desirable, either, because, in such a case, even small targets which are not to be considered would be acquired and a considerably increased ground noise would result, a sharply focused radar lobe with a certain lobe width is used for the direction finding. However, within this radar lobe, the Poynting's vectors are variable, so that, in the direction of the symmetry axis of the lobe, the sensitivity of the angle-measuring shows a maximum, with the sensitivity decreasing toward the borders of the lobe. Thus, for a target acquired at the border of the radar lobe, the signal-to-noise ratio is unfavorable. In addition, there after errors due to the reference systems of the missile, for example to the zero variations, drifts, or both of the gyroscopic devices used in the inertial system.
This is why a blur is associated with such an angle measurement, with the result that a recognition of a decoy, located laterally and vertically away from the target, is not possible before the missile is only a small distance from the decoy. For this reason, an evaluation of the "elevation criterion" by the airborne logic circuits of the missile may be effected, but, after a certain time of flight and too late for the desired purpose.
Within the range utilizable for the angle measurement, which approximately begins 4 km before the target, it would be necessary to interrupt the target homing as soon as it is found out that, up to the time, the missile has been following a decoy. After a new target search and setting of the search head upon the newly found target, the missile must be angularly accelerated transversely relative to its trajectory, in accordance with the angular deviation of the new target, in order to bring the missile back into a collision course with the target. However, in view of the fact that the decoys generally are located several hundred meters away from the true target, in most cases, the necessary transverse accelerations can no longer be imparted, so that the missile will miss the true target.